Convex-surfaced vacuum controlled air film



Sept. 2, 1969 I J. A. WEIDENHAMMER ETAL 3,465,320

CONVEX-SURFACED VACUUM CONTROLLED AIR FILM Filed Jan. 10, 1966 3Sheets-Sheet 1 INVENTORS JAMES A. WEIDENHAMMER EDWARD J. WROBLEWSKIRAYMOND A. BARBEAU ATTORNEY p 2, 1969 J. A. WEIDENHAMMER ET AL 3,465,320

CONVEX-SURFACED VACUUM CONTROLLED AIR FILM I Fiiad aan. 1d, 1966 s sheet-sheet 2 LATERAL 5 HEAD POSITIONING MEANS, HEAD BRUSH I CONNECTIONS,

AND

52 DRIVE MOTOR p 1969 J. A. WEIDENHAMMER ETAL 3,

CONVEX-SURFACED VACUUM CONTROLLED AIR FILM Filed Jan. 10, 1966 3Sheets-Sheet s LATERAL HEAD POSITIONlNG MEANS,

AIR SOURCES HEAD BRUSH CONNECTIONS.

ANGULAR LENGTH OF 31m? United States Patent 3,465,320 CONVEX-SURFACEDVACUUM CONTROLLED AIR FILM James A. Weidenhammer, Edward I. Wroblewski,and

Raymond A. Barbeau, Poughkeepsie, N.Y., assignors to InternationalBusiness Machines Corporation, Armonk, N.Y., a corporation of New YorkFiled Jan. 10, 1966, Ser. No. 519,788 Int. Cl. Gllb 5/00; B65h 17/32 US.Cl. 340-1741 8 Claims ABSTRACT OF THE DISCLOSURE A convexcontrolled-spaced area over which a web is moved with only a thin airfilm lubricating separation.

The convex controlled-spaced area has a magnetic transducer smoothlyembedded therein and is bounded on a leading side by one or more vacuumports and is optionally bounded on its lagging side by one or moreblowing air ports. Vacuum ports may be provided on opposite sides of thearea for bidirectional relative movement; or blowing air and vacuum maybe reversed for bidirectional relative motion, since only the leadingports are required to have vacuum. With long angular length webs (havingmore than about 100 angle-ofwrap about the convex surface), laggingblowing air ports prevent excessive tension and wear on the initialangular portion of the web. The convex controlled-spaced area requires asmoothness factor that is inter-related with the spacing (h*) betweenthe area and the web.

This invention relates generally to the spacing control between acontinuously-smooth convex-surfaced area and a flexible web havingrelative motion. In particular, the convex surface can be moved relativeto the web with a separation in the order of tens of microinches. Suchclose spacing enhances recording communications between them when theweb has a recording surface in electrostatic or electromagneticrelationship with a transducer smoothly embedded in the convex-surfacedarea.

Prior devices involving magnetic heads in relation to magnetic tape haveutilized a hydrodynamic laminar air boundary to lubricate the frictionalengagement between surfaces with a spacing in the order of hundreds ofmicroinches. The relatively moving surfaces carry air molecules betweenthem causing them to be spaced by a distance dependent upon a number ofvariables such as the relative velocity between the surfaces, thetension between them, the coeflicient of friction of the surfaces, andother factors. Blowing air between the surfaces has also been used tocontrol this spacing relationship. In neither the hydrodynamic nor theblowing air techniques is the spacing between a web and a relativelymoving surface made sufficiently small and controllable for the highdensity recording and sensing techniques found in todays magneticrecording apparatus involving bit densities in excess of three thousandsbits per inch.

This invention relates generally to a discovered species within thetechnique described and claimed in IBM owned Patent No. 3,327,916 withthe title Vacupm Controlled Air Film by inventors R. A. Barbeau, D. K.Close, K. B. Day, In, E. I. Wroblewski and J. A. Weidenhammer.

It is therefore the primary object of this invention to provide gaslubrication control between a relatively moving web and convex surfaceto maintain a precisely-controlled stable spacing (such as within plusor minus ten millionths of an inch of a required spacing) between themover a selected area of the convex element during relative movement.

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It is another object of this invention to provide an air lubricationarrangement between a relatively moving web and a portion of acylindrical surface to obtain precise spacing control between the weband the portion of the surface to enable very high density recording orreading operations between them.

It is a further object of this invention to provide a rotating surfacehaving a flexible strip wrapped around a portion of it, wherein aprecise spacing is maintained between a selected area on the rotatingsurface and the web, with the spacing being independent of either theangular position of the selected area, or the angular length of thestrip about the rotating surface.

It is still another object of this invention to provide a rotatingsurface in relation to a web wrapped partly about it using a vacuumtechnique to control a precise spacing between the rotating surface andthe web over an area following the vacuum ports and to prevent severetension on initial web portions.

It is another object of this invention to provide means for obtaining aconstant spacing between a recording strip and a controlled-spaced areaon a rotating drum by providing vacuum control prior to said controlledspaced area and by providing blowing air after said area.

It is another object of this invention to provide means for preventingsignificant varying tension on a strip having a substantial angularlength about a rotating surface and a very close non-touchingrelationship.

It is another object of this invention to magnetically write and/ orread a high density digital signal between a rotating surface and a webwrapped in excess of about said rotating surface by using pneumaticvacuum control prior to and pneumatic pressure control following acontrolled-spaced area having a transducer to obtain constant spacingand to avoid any possibility of rubbing contact.

It is a further object of this invention to provide a cyclicallyoperating rotating surface containing a transducer enabling thetransducer to have high density flux communication with a web for anyangular length of said web up to 360 about the rotating surface and forevery angular position of said transducer within said angular lengthwithout any rubbing contact between them.

In order to accomplish the objects of this invention a convexcontrolled-spaced area is provided having a smooth continuously convexsurface with vacuum ports formed through a leading part of thesmooth-convex surface prior to the controlled-spaced area over whichsaid web is to be precisely spaced. A flux transducer may be mounted insaid controlled-spaced area; but it must not interrupt the smooth convexcontour. For bidirectional relative movement between the web and convexcontrolled-spaced area," vacuum ports are provided on opposite sides ofthe area, since each opposite side is a leading port of the area for onedirection of movement. This invention also may provide blowing air tothe lagging ports (following the controlled-spaced area in a particulardirection of relative movement), since only the leading ports arerequired to have vacuum for operating the controlled-spaced area. Thelagging blowing air ports obtain increased spacing between the surfacesoutside the controlled-spaced area to prevent rubbing of the web on apossible non-smooth surface outside the controlled-spaced area. Withlong angular length webs (having more than about 100 angle-of-wrap aboutthe convex surface), the lagging blowing air ports also preventexcessive tension and wear over the initial angular portion of the web.The convex controlledspaced area requires a surface with a smoothnessfactor that is inter-related with the smoothness factor of the facingsurface of the web and spacing (11*) between them. The sum of the twosmoothness factors is approximately equal to one-half of 11*.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of the preferred embodiments of the invention, asillustrated in the accompanying drawings.

FIG. 1 is a perspective view of a strip-file embodying the invention.

FIG. 2 shows a partial cross-section through section 22 in FIG. 1 withan elevational view of a drum member therein.

FIG. 3 represents a schematic view of section 33 found in FIG. 2.

FIG. 4 represents another embodiment having the invention.

FIG. 5 illustrates a sliding connection between a rotating member and asupporting shaft related to the embodiments in FIGS. 2 and 4.

FIG. 6 shows pneumatic vacuum and pressure communication fromnon-rotatable tubes to headers Within a rotatable shaft.

FIG. 7 illustrates another embodiment of the subject invention.

FIG. 8 shows diagrams used in explaining certain operationcharacteristics of the invention.

The subject invention involves the discovery that the principles of theflat vacuum surface for obtaining a controlled spacing h*, which isdescribed and claimed in patent application Ser. No. 463,727, is alsoapplicable to a convex continuously-smooth surface operating with arelatively moving web. The convex species of the controlled-vacuumsurface is described and claimed herein. It has also been discoveredthat certain additional problems exist with operation of this inventionspecies when it is incorporated in a rotating drum or otherwise involvesa long angular length; and means has been discovered for solving theseproblems which is described and claimed herein.

FIG. 1 shows an embodiment of a strip-file arrangement in which aplurality of strip-file cartridges 10 (which may be removable andinterchangeable) are tangentially arranged about a processing chamber 28through which the end of a rotating shaft 24 is visible. Each cartridge10 includes a web or strip 11. The edges of strip 11 are supported onopposite sides by slots 12 within cartridge 11. The web comprising strip11 may be made from Mylar Polyester Film (Du Pont trademark) or somecomparable flexible plastic or metal structure. One of both sides mayhave a recording surface applied thereon, such as iron oxide or othermagnetic particles supported in binder, or cobalt nickel or othermagnetic materials plated thereon, either electrolessly or electrically.

A piston 13 is provided at the outer end of strip 11, and it may be madeof the same material from which the strip is made. Piston 13substantially fills the entire crosssectional opening in cartridge '10engaged by it.

A minimum-size plenum chamber 15 is provided at the outer end of eachcarriage 10. Air conveyance tubes 18 and 19 connect to each plenum 15.Tube 18 connects to a vacuum source and tube 19 connects a pressuresource of air. Electromagnetically-actuated valves 61 and 62 communicatewith plenum 15 and connect to the respective tubes 18 and 19. Each valvemay be constructed as the High Speed Valve disclosed on page of theOctober 1963 issue of the IBM Technical Disclosure Bulletin. Valve 61controls the vacuum V (below-atmospheric pressure) to plenum 15 fromtube 18 and is operated by an electrical cable 57; a similar valve 62controls the application of pressure P (above-atmospheric pressure) toplenum 15 and is controlled by electrical cable 58. Thus, electricalenergization of cable 58 opens valve 62 to connect pressure from tube 19to plenum 15 which drives piston 13 away from the plenum to move the endof strip 11 out of the cartridge into the processing chamber 28. Cable58 can be de-cnergized immediately after the end of the strip isreceived by chamber 28, since the normal operation of processing chamber28 causes the strip to be maintained in this outward position. Afterprocessing, the strip can be retrieved within the cartridge 10 byenergizing cable 57 which opens valve 61 at the end of tube 18 andconnects plenum 15 to the vacuum source, which lowers the pressure onpiston 13 forcing it to move back to its original position at the outerend of the cartridge, pulling strip 11 out of the processing chambersimultaneously. When the strip is moved back to its normal storageposition in cartridge 10, the energiza tion of cable 57 can bediscontinued so that valve 18 may be closed. Thus, both valves may benormally closed and in a normally deenergized condition when its strip11 is not being moved in or out of the cartridge.

A controlled-spaced area on a rotating drum 21 in processing chamber 28is revealed in FIG. 2 including the two sets of slots 23 and 29. A drum21 is supported by a shaft 24 that extends through the side walls ofchamber 28 and is supported rotationally therein by ball bearings. Thecontrolled-spaced area on the surface of drum 26 has smoothly embeddedwithin it a plurality of electromagnetic recording or reading head gaps22a n, useful for writing or reading magnetically recorded data onplural tracks of any strip 10. Such head gaps are conventional in theart, and any of the wellknown narrow-gap types may be used for recordingor reading high-density digital information. Such gaps are filled withnon-magnetic material.

A plurality of slots 23 are formed through the leading portion of thecontrolled-spaced area, and these slots are connected to a vacuumsource. Another plurality of slots 29 are formed through the laggingportion of the contr0lled-spaced area, and these slots are connected toa pressurized air source.

The controlled-spaced area in this invention only includes the part ofthe convex surface required for 0htaining the precisely controlledsurface-to-web spacing operation. The controlled-spaced area generallyextends only for a fraction of 360 over the convex surface, and it isrepresented for example by the angles M and N in FIGS. 3 and 7,respectively. The limits of the controlled-spaced area need extend onlyfor a short distance for example, about one-half inch) before the firstvacuum slot 23 (away from the controlled-spaced area) to the oppositeside of the controlled-spaced area that may be extended as far asrequired about the drum (up to 360). This smooth convex surface for thecontrolled-spaced area is smooth to approximately 20 millionths of aninch or less, which distinguishes it from the remainder of the drumsurface which need not be smooth to within this tolerance. The preciseamount of smoothness tolerance required for the surface of thecontrolled-spaced area is inter-related with the smoothness on the websurface facing it. The actual smoothness limits on the web and thecontrolled-spaced area is inter-related as follows: the sum of theactual smoothness limits on both the controlled-spaced area and itsfacing web surface is equal to approximately one-half of the spacing(12*) between them, which is controlled by the vacuum ports.

When blowing jets 29 are used, the first jet 29 adjacent to thecontrolled-spaced area may be considered to terminate thecontrolled-spaced area.

In FIG. 3, shaft 24 is constructed to have separate internalcoaxially-arranged air headers 46 and 47. Header 47 may conveypressurized air while header 46 conveys vacuumized air (belowatmospheric pressure). A channel 31 through drum 21 connects header 47to a plenum distribution chamber 33 connecting to slots 29. Similarly,channel 32 connects header 46 to plenum 34 to convey vacuumized air toslots 23. An opening is provided through the wall of plenum 34 toatmospheric pressure. Opening 80 reduces any variations in vacuumpressure at slots 23 caused by fluctuation in the vacuum pressure of thesource (not shown).

FIG. 6 shows a technique for conveying pressurized and vacuumized air tothe respective coaxial headers within shaft 24. A tube 51 is connectedbetween a chamber 36 and a conventional vacuum source (not shown)supplying for example a pressure of 10 inches of water below atmosphericpressure. Similarly a tube 52 is connected between a separate chamber 37and a conventional pressurized source (not shown). Cylindricalnonrotatable chambers 36 surround a part of rotatable shaft 24; and theyare isolated from each other. Chamber 36 pneumatically communicates witha plurality of openings 48 through the wall of hollow shaft 24. Openings48 are aligned circumferentially about shaft 24, and they enable thevacuumized air within chamber 36 to communicate with the vacuum coaxialheader 46. In a similar manner, a plurality of circumferentially-alignedopenings 49 are cut through another portion of shaft 24 in a circularpattern for communicating the pressurized air from chamber 37 to theinner coaxial header 47. To do this, the inner coaxial header 47terminates by flaring out to the outer edge of shaft 24 with a barricade38 which terminates the outer coaxial header 46. A wall 39 similarlyterminates header 47 on the right in FIG. 6. A butterfly valve 81 isplaced within tube 51 to add serial resistance to the pneumatic vacuumpath to further isolate source fluctuations in the vacuum pressure fromvacuum pressure at slots 23.

As shown in FIG. 2, a motor 50 drives shaft 24 to rotate drum 21 at aconstant rotational velocity in the counterclockwise direction of thearrow shown in FIGS. 3 or 7.

Strip 11, shown in FIG. 3, may be obtained from any of the cartridges10, shown in FIG. 1, by energizing electrically cable 58 to open thevalve connecting the pressure source from tube 19 to plenum 15.

As soon as the end of the strip 11 is moved into slightfrictional-pneumatic engagement with rotating drum 21, the air movementtangentially from the drum in the direction of the arrow exerts a forceon the end of the strip tending to pull it from the cartridge anddecreasing the access time of strip over and above the actuation solelyprovided by piston 13 being actuated by the pressure source. Strip 11may have any angular length (A.L.) of wrap about the drum between 0 and360. FIG. 3 shows a single strip with about a 300 angular length. FIG. 7shows a plurality of strips 11a, 11b, 11c each with an angular length(A.L.) of about 100 and being simultaneously processed. When pluralstrips are processed, each strip can have an angular length (A.L.) up to360/K where K is the number of strips being simultaneously processed.

FIG. 3 shows the position of strip 11 about drum 21 after piston 13 hasmoved to a bottom extreme position in cartridge 10. In principle, theangular length (A.L.) of strip 11 can be controlled by piston -13 tohave a shorter A.L. or even a variable A.L. up to the full extension ofthe strip. In fact, any strip 11 can be processed while it is movingtoward its fully extended position. In extended position shown, theinner side of the strip contains a magnetic recording surface which maybe recorded upon or read from by means of any or all magnetic write/readhead gaps 22a n' which may be the type used for writing or reading upona conventional magnetic surface, such as tape, drum or disk. Hence, anystrip 11 can be processed while head gaps 22 are sweeping along all orpart of its angular length.

The moving surface of drum 21 frictionally engages air molecules andcarries them along to create a laminar air boundary between the convexcylindrical surface and the angular length of strip 11. No portion ofstrip 11 makes actual rubbing contact with the surface of drum 21.

Without the vacuum pressure on the drum surface, the laminar air filmabout the drum surface would cause excessive spacing of strip 1 1 fromthe drum surface making high density writing or reading of digital dataon the strip impossible.

In the absence of any vacuum pressure at slots 23, any strip 11 ofwhatever length being moved toward the rotating drum would not be drawntoward the drum surface. This is because the normal movement of airabout the drum surface causes centrifugal outward air movement tendingto blow the strip away from the drum. Thus, circumferential andtangential grooves 27 are provided to guide each strip 11 about thedrum. Grooves 27 loosely support each strip 11, and they tangentiallyconnect to grooves 12 in cartridges 10. The outward guidance of a strip11 along opposite grooves 27 is aided by the circumferential air flowabout the drum in its direction of rotation. This air movement createsan outward tension on the strip which causes the strip to move outwardlyalong opposite grooves 27 without any required assistance from vacuumports 23 at a speed less than the drum surface velocity. The vacuumports obtain a closer pneumatic-frictional engagement between therotating drum surface and a web being extended to further aid the speedof the extending operation.

With only vacuum applied to slots 23, and no pressure applied to slots29, the close spacing 11* (shown in FIG. 8) precisely exists betweenstrip 11 and the controled-spaced area, as long as the angular length ofstrip does not exceed about in the embodiment. In this case, 11* issubstantially constant for all angular positions of the transducerwithin any angular length. The controlled-spaced area extends behind thevacuum slots until an interruption occurs in the smooth-convex surfacecomprising the controlled-spaced area.

The force on strip 11 increases as the air film thickness h is madesmaller, and/or the size of the controlledspaced area is made larger.Thus, the force increase as the length of the h* spaced area is madelonger, or by increasing the vacuum pressure at slots 23 to decrease h*.

The force on strip 11 is maximum at the initial point T (in FIG. 3) ofthe angular length; and the force decreases to zero at the final point Dof the angular length. The maximum tension within the angular length ofan operating strip 11 thus exists along its initial portion at and nearthe initial point T. The tension on this initial portion of the stripincreases as its angular length about drum 21 is increased, otherparameters remaining unchanged. Accordingly, the more the angle of wrap,the greater becomes the total molecular drag; and thus the greaterbecomes the pull at the point of entry T, and tension on the stripdecreases along the strip as the end of strip D is approached. When theangular length exceeds about 120 with no blowing air slots 29, but withvacuum slots 23 operating, the tension forces along the initial portionof the angular length may increase to the point where air spacing theremay decrease undesirably as represented by curve Q in FIG. 8. In otherwords, an increase in angular length beyond about 120 increases thevarying tension about the initial angular length to the degree that theincreased force squeezes the air film so that spacing at thecontrolled-spaced area reduces up to the beginning T of the strip asshown by curve Q in FIG. 8.

This initial spacing variation can have very detrimental etfects on theoperation of a long strip 11 by causing premature wear failure on itsinitial angular length portion, where the spacing Q in FIG. 8 is sosmall that roughness on the drum surface or small moving particles inthe air can catch abrasively between the surfaces to destroy thisinitial web surface. Even for short strips (between 0 and 120 angularlength), premature wear may be caused over an entire strip surface byundesired rubring of rough surfaces on the drum outside an area beingdesignated as the controlled-spaced area, which may be the only area onthe drum machined to the smoothness needed for reliable operation with anarrow air spacing 11*. If the remainder of the drum surface is notmachined to the same order of microninch smoothness, peak roughnesspoints may penetrate the h spacing to wear quickly along the entireangular length of strip 1 1.

In addition to obtaining a precisely small strip spacing 11*, thisinvention also alleviates all of the abovementioned problems resultingfrom (1) having 11* too small at initial portions of a long angularlength, or (2) obtaining [2* along rough surfaces of drum 21 outside ofa uniquely defined controlled-spaced area. This invention alleviatesthese problems by providing blowing air ports 29 following the vacuumcontrolled-spaced area for increasing the air film thickness to muchgreater than 12* for drum areas outside of the controlled-spaced area toextend the useful life of a strip of any angular length and to preventundue initial tension on any strip of large angular length (120 ormore).

The evacuating operation at the leading ports 23 causes a substantiallyconstant spacing 11* to exist between the web and the controlled-spacedarea following ports 23. The amount of spacing [1* is a function of thenumber of ports their size, spacing, and the amount of vacuum applied atthe ports. Spacing 12* can be regulated easily by controlling the vacuumpressure to ports 23.

Although ports 23 are shown as slots, they may be openings of any shape,such as a series of small holes, as long as the openings are generallypositioned in the locations of slots 23 and 29, so that theyrespectively lead and lag in the controlled-spaced area. Such openingscannot exist either through or laterally along either or both sides ofthe controlled-spaced area, which would destroy the uniformity ofspacing 11*.

Slots 29 in FIG. 3 eject blowing air to increase the spacing S followingthe controlled-spaced area. The spacing S before the controlled-spacearea is also large due to the cyclic operation of slots 29. After slots29 have left a strip, it is left with the relatively large spacing Sbetween it and the drum surface compared to the smaller spacing 11*.

This large spacing S does not significantly change by the time thevacuum slots 23 begin their next sweep of the angular length, since airleakage along the edges of the strip is not significant within the shortcyclic period involved with, for example, 1800 revolutions per minute ofthe drum. Hence, the spacing S existing ahead of the controlled-spacedarea is a result of the cyclic operation of this embodiment.

In more detail, with both vacuumized slots 23 and pressurized slots 29operating, a dynamic pneumatic operation occurs in the spacing betweenthe angular length of strip 11 and rotating drum 21, with respect to thecycled evacuation and ejection of air by slots 23 and 29. Spacing 11*over the controlled-spaced area remains constant as shown in FIG. 8.However, at the trailing edge of the controlled-spaced area, the blowingair from jets 29 creates the much larger and somewhat variable spacing Swhich is a point falling in the cross-hatched area in FIG. 8. Spacing Svaries somewhat with the angular length of the strip 11 and with theangular position of the controlled-spaced area. For any particularangular length for a strip 11, spacing S varies within a range R shownin FIG. 8, which is a vertical line at the abscissa value representingthe angular length of the strip. Range R is bounded by lines S and S inFIG. 8. Curve S represents the limit of the spacing S at the beginning Tof the angular length; and curve S represents the opposite limit ofspacing S at the end D of strip 11. The reason for the variation ofcurve S with angular length is because tension at the beginning of theangular length increases with the size of the angular length, whichcorrespondingly de creases the spacing S along the initial portions forlonger angular length strips. Surprisingly, this tension variation doesnot appear to effect the controlled spacing lz On the other hand, a lackof tension at the end of the angular length prevents this factor fromaffecting the spacing S which may even increase very slightly with anincrease in angular length.

Thus slots 29 restore a thick film of air after the controlled-spacedarea to eliminate any windless squeezing of the strip about the drum,particularly about the highest tensioned initial angular length.Accordingly, this invention permits reliable reading and writing onsubstantially the entire angular length of the strip about drum 21 atvery high data density, because spacing h* can be precisely controlledto a very small amount, without resulting in any detrimental effects onstrip 11 due to roughness on the drum outside the controlled-spaced areaor due to large angular lengths.

If relative movement between the web and drum is stopped in FIG. 3,spacing control would be lost, since the h spacing would collapse withthe web drawn to the vacuumized slots. Hence, control of spacing hdepends on maintaining relative movement. If the speed in movement ischanged, a compensating change is needed in the vacuum pressure at slots23 to equalize 11*.

As previously mentioned, a plurality of strips can be processedsimultaneously. For example, the three strips shown in FIG. 7 aresimultaneously handled by drum 21, that is all strips can haveinformation written or read during a single rotational cycle of thedrum. In FIG. 7, each of the strips 11a, 11b, 11c has an angular lengthwhich is sufficiently small (less than that it does not have asubstantial force affecting h at the beginning of its angular lengthwhen there are no blowing air ports 29 following the controlled-spacedarea. Hence, in the case of small angular length strips, the trailingblowing air slots 29 may be eliminated leaving only the vacuum slots 23to obtain the required controlled small spacing 11*. Thus, in the caseof FIG. 7, curve Q in FIG. 8 does not exist even without blowing airports 29. The lack of blowing air ports in FIG. 7 extends thecontrolled-spaced area to the first discontinuity following the vacuumports 23, which is the initial point T of the angular length for eachstrip. The spacing 11* is obtained therefore throughout the angularlength of each strip. This results in requiring the entire surface ofthe drum to have the smoothness requirements of the controlled-spacedarea, in order to obtain long life for the strips. This situation withthe embodiment in FIG. 7 is contrasted with the embodiment in FIG. 3where only the drum surface between and including slots 23 and 29 needhave the precise smoothness tolerances needed for the controlled-spacedarea, regardless of whether it is used with only the single strip shownin FIG. 3 or with plural strips as shown in FIG. 7.

In the embodiments thus far discussed with respect to FIGS. 2, 3 and 7,it is presumed that there are a plurality of heads positioned across thedrum so that any of plural lateral recording tracks on a strip can beWriten or read by electronically switching among the different laterallydisplaced heads 22a 12. However, in some circumstances, it may bedesirable to have only a single head which is laterally positionableamong plural tracks on a strip (or strips). This situation isrepresented by the embodiment shown in FIG. 4 having a single head gap42 (or a few head gaps) supported on a drum 61 of the same type as drum21 in FIG. 2, except that drum 61 is thinner and is laterally movablefor aligning the head with different tracks on a strip. Either drumcross-section represented by FIG. 3 or 7 can represent a cross-sectionof FIG. 2 to provide vacuum ports (like 23) only or in combination withblowing air ports (like 29).

Likewise in FIG. 4, vacuum slots 43 precede the controlled-spaced areawhich includes head gap 42. Slots 47 emit pressurized air following thecontrolled-spaced are. Thus a precise spacing 11* is obtained at headgap 42 in the same manner as explained for obtaining the 9 [precisespacing h* at the head gaps 22a n in FIG. 2.

In FIG. 4, a box 56 represents a lateral head positioning means, headbrush connections, and the drive motor. The drive motor may be identicalto motor 50, and the brush connections may be identical to the brushconnections 53 provided in FIG. 2. Pneumatic chambers 36 and 37 likewisecommunicate with ports 43 and 47. The lateral positioning of drum 21 inFIG. 4 may be accomplished in any of several ways. The lateral headpositioning means may be similar to the head positioning meansconventionally provided on disc drives, such as the IBM 1311 disc drivefor positioning a head inwardly or outwardly upon computer command foraccessing a selected track. Head positioning means also is beingcommercially used on drum files and on strip files, for example, in theIBM 232.1 data cell drive.

It is also possible to have the strip laterally positioned instead ofthe drum in order to obtain lateral track accessing, and this is amatter of expediency in the particular design of the system.

In FIG. 4, shaft 24 is laterally slideable within bearings 78 and 79supporting the shaft in processing chamber 28. Another arrangement isshown in FIG. 5, which allows shaft 24 to be laterally fixed in bearings78 and 79, in the manner shown in FIG. 2. Thus, in FIG. 5, shaft 24 ishollow and receives within it a laterally slideable shaft 62 to which isatached drum 61. Hence, drum 61 is laterally slideable on shaft 24. Drum61 is fastened to shaft 62 by keys 64 and 65 received in keyways formedin drum 61 and in a solid portion 63 of shaft 62. Keys 64 and 65 passthrough and slideably engage slots 66 and 67 formed throughdiametrically opposite sides of hollow shaft 24. The amount of lateralmovement for shaft 62 is determined by the length slots 66 and 67 inshaft 24.

In FIG. 5 motor 50 drives shaft 24 by means of gears 68 and 69, whereingear 69 is fixed directly to shaft 24; and they are independent of thehead positioning means. In this case, the head positioning means,pressure and vacuum air sources, and brush connections are representedby box 76, and they are connected directly to shaft 62. The air sourceconnection shown in FIG. 6 may be used in FIG. 5. The brush connectionsand lead arrangements to the head are not shown but are well known inthe art, such as those commercially used on video tape recorders havingrotating heads.

The strip file shown in FIG. 1 may include as many cartridges as canfeasibly be placed at respective tangential positions about the rotatingdrum. The cartridges may be made removable, replaceable andinterchangeable, so that the strip file device can have a library ofinterchangeable cartridges.

The vacuumized convex-surfaced spacing-control feature of this inventionis usable wherever there is relative movement between the web and thevacuumized convex surface. Thus, the embodiment previously described maybe used in the reverse sense. That is, the drum 21 may be heldstationary while the strip is moved past head gap 22 under actuation ofpiston 13. For bidirectional control of spacing 11*, slots 23 and 29have their air sources reversed, so that the vacuum pressure is alwaysapplied to the leading ports for any direction of movement.Alternatively, vacuum can be applied to both sets of slots 23 and 2.9for bidirectional relative motion between the web and thecontrolled-spaced area. A further practical extension of this samesituation is to use an elongated web, such as conventional magnetic tapepassing from reel-toreel, instead of strip 11 in FIG. 3. In the lattercase, vacuum is applied to both sets of ports 23 and 29; and the angularlength of the web need only be sufiicient to encompass both sets ofslots. In this case, the remainder of the drum surface can be eliminatedto the right of dashed line 91 in FIG. 3.

The ports 23, 43, 29 and 47 in FIGS. 2 and 4 may also be represented bya plurality of small round holes having a diameter substantiallyequivalent to the width of slots 23 and 29 or 43 and 47 and located inthe leading or lagging positions represented by ports 23, 43 or 29, 47,respectively in order to obtain substantially the same type ofperformance. Slots appear to give optimum performance, but other shapedholes may give satisfactory performance, and round holes are easier tomake and hence may be more economic.

In either FIG. 3 or 7, it has been found that a plurality of slots ineach group 23 and 29, or 43 and 47 operate better than having a singleslot representing each group. It has been found that with a plurality oflongitudinallydisplaced slots in each group, variation in thevacuumsource pressure does not affect the controlled spacing h* to thedegree affected by a single slot in each group.

Multiple controlled-spaced areas, each with its head gaps, its vacuumports 23 and pressure slots 29 may be provided at different angularlocations about a single drum used with either a single strip as in FIG.3, or with simultaneous strips as in FIG. 7, in order to shorten theaccess time :to different parts of the same strip or to differentsimultaneous strips, without increasing the rotational velocity of thedrum. Of course, the rotational velocity alone can be increased toshorten the access time.

This application is related to patent application having U.S. Ser. No.519,570, filed on Jan. 10, 1966 now Patent No. 3,420,424 by R. A.Barbeau, K. B. Day, J1. and J. A. Weidenhammer.

What is claimed is:

1. Spacing control means between a flexible web and a transducerincluding a convex surface having formed thereon a smoothcontrolled-spaced area surrounding said transducer, at least one vacuumport being formed through a leading side of said controlled-spaced area,

means for providing relative movement between said web and saidcontrolled-spaced area,

an air film bearing with a thickness of the order of tens of microinchesbeing the only separation between said relatively moving web and saidconvex surface,

said controlled-spaced area extending from said vacuum port to a firstinterruption in smoothness continuity for said area,

the smoothness factor of said convex controlledspaced area being to anorder of microinches,

and at least one blowing air port following said controlled-spaced areain the direction of relative movement,

whereby said transducer can communicate flux between said non-contactingconvex controlled-spaced area and said web with only said air filmbearing intervening.

2. Spacing control means between a flexible web and a transducerincluding a convex surface having formed thereon a smoothcontrolled-spaced area surrounding said transducer, at least one vacuumport being formed through a leading side of said controlled-spaced area,

means for providing relative movement between said web and saidcontrolled-spaced area, an air film bearing with a thickness of theorder of tens of microinches being the only separation between saidrelatively moving web and said convex surface,

said controlled-spaced area extending from said vacuum port to a firstinterruption in smoothness continuity for said area,

the smoothness factor of said convex controlled-spaced area being to anorder of microinches,

and said convex controlled-spaced area being a part of a surface of arotatable cylinder.

3. Convex air-bearing means as defined in claim 2 in which websupporting means comprises opposite grooved members having a spacedcircumferential relationship around at least a portion of said cylinderfor supporting said web about its angular length for relative rotationby said controlled-spaced area.

4. Convex air-bearing means as defined in claim 3 which further includesmeans for moving said Web into said opposite grooved members to providean angular length about the surface of said drum.

5. Convex air-bearing means including a convex surface having formedthereon a smooth controlled-spaced area,

at least one vacuum port being formed through a leading side of saidcontrolled-spaced area,

said controlled-spaced area extending to a first interruption insmoothness continuity for said area following said vacuum port,

a drum for supporting rotatably said controlled-spaced area,

means for providing relative motion between said convex surface and aweb,

the direction of said relative motion being to carry any point on saidweb over said surface from said ports to said controlled-spaced area,whereby said Web moves over said controlled-spaced area behind saidvacuum ports with a stable and precisely controllable spacing therefrom,

means for supporting-the web with an angular length about said rotatablemeans,

means for supporting a plurality of webs about said drum in positionshaving no angular length about said rotatable means,

and means for selecting at least one web at a time for movement to aposition of angular length about said drum.

6. Convex air-bearing means as defined in claim 5 further includingmeans for operating said air-bearing means with a plurality of said webbeing selected.

7. A strip file device comprising a storage pocket containing a striphaving a magnetic surface, with a piston formed at an outer end of saidstrip,

means located at the outer end of said pocket for communicating high andlow pressure air for moving said strip in and out of said pocket,

a rotating drum having its surface tangentially arranged with respect tosaid strip,

at least one head located in said drum with a recording gap flush withat least a smoothly-defined portion of the surface of said drum,

and means for applying a vacuum pressure through the smoothly-definedportion of the surface of said drum prior to said head gap.

8. A strip file device as defined in claim 7 further including means forapplying above-atmospheric pressure through the surface of said drumafter said recording gap.

References Cited UNITED STATES PATENTS 3,151,796 10/1964 Lipschutz226-97 3,125,265 3/1964 Warren 226- X FOREIGN PATENTS 952,697 3/1964Great Britain.

M. HENSON WOOD, 1a., Primary Examiner R. A. SCHACHER, Assistant ExaminerUS. Cl. X.R.

